The Circulatory System

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How tissue fluid is formed

1. At the start of the capillary bed, nearest to the arteries, the pressure is greater in the capillaries than in the tissue fluid

2. This difference in pressure forces fluid out of the capillaries and into the spaces around the cells, forming tissue fluid. Proteins and other large molecules stay in the capillaries

3. This means that the pressure is much lower at the end of the capillary bed thats nearest to the veins.

4. Due to the fluid loss, the water potential at the end of the capillaries nearest the veins is lower than that of the tissue fluid

5. As a result, some water re-enters the capillaries from the tissue fluid at the vein end by osmosis

6. The lymph system collects any excess tissue fluid.

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Arteries- adaptations

  • They carry  blood from the heart to the rest of the body
  • thick and muscular walls- to cope with the high pressures produced by the heartbeat
  • also have lots of elastic fibres
  • The inner lining is folded- this allows the artery to stretch, whic also helps to cope with high pressure
  • They contract when the blood flows through them, then they recoil once the blood has moved on. This prevents the arteries from bursting
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